CAREER: The Role of Relative Motion and Intermolecular Ordering on Dynamic Behavior of Polymers and Polymer Blends

本研究项目的目标是：(1)将玻璃形成聚合物弛豫过程中的相对运动与分子间和分子内堆积的特征联系起来；(2)评估分子间堆积随环境变化的方式，以及这些变化与共混物弛豫行为的关系。先前已经证明了与首选分子间填充距离相对应的空间区域的重要性。然而，并不是所有的聚合物都有相似程度的分子间有序，这对动力学的影响是未知的。此外，分子间排序随环境的变化而变化，其影响也是未知的。为了实现上述目标，将考虑一系列聚合物，其中分子间有序程度从很少到广泛不等。一个给定的聚合物[A]将被考虑在一系列的第二组分[B]中。观察分子间有序程度的变化，包括原聚合物[A-A]和环境变化诱导的新有序[A-B}。观测将通过相干中子散射进行，它揭示了在选定的空间尺度上的相对运动，分子模拟将评估与链间堆积相关的空间分离的位置和程度。之所以选择这种技术组合，是因为它们可以跟随具有空间选择性的相对运动。利用中子测量在空间尺度上的选择能力来分离a和b弛豫的贡献，并分别评估环境对它们的影响。该方案的新颖之处在于遵循相对运动，而不是自我运动，研究精心挑选的一系列材料，并整合分子模拟。这项工作完成后，将使我们能够将分子间堆积的特征与相对运动联系起来，并明确地描绘环境在混相混合动力学中的作用。教育活动的中心是把研究型活动带给学生，否则他们就不会有这些经历。具体而言，开放式实验/模拟问题将引入核心化学工程课程，为非研究型大学的学生提供研究机会，并在化学工程课程中增加分子模拟及其在实验中的作用的高级选修课程。加州波莫纳理工学院（calpoly Pomona）是一所没有正式研究项目的工业导向型大学，将邀请即将进入大四的被选中的本科生在PI的小组中进行一个夏天的研究。学生的研究将在最后一年作为他们的毕业论文项目继续进行。这些学生将根据他们在宾夕法尼亚州立大学进行的研究开发一个课程项目。同时，在反应工程和热力学课程中开发开放式项目，并在高级实验课程中增加模拟实验。这些项目将被编译，并在计划的最后一年，作为高级选修课程的模块。本课程针对非模拟器，将教学生如何使用和解释模拟数据，就像传统的实验课程对实验数据做同样的事情一样。本提案中要进行的研究属于聚合物熔体和共混物的短期动态行为的一般领域，这一领域与这些常见材料的玻璃化转变和加工行为相关。

The objectives of this research project are to (1) correlate relative motion in relaxation processes of glass-forming polymers with the character of inter- and intra-molecular packing, and (2) assess the way in which intermolecular packing changes as a function of environment and the relation of these changes to know relaxation behavior in blends. The importance of the spatial region corresponding to the preferred intermolecular packing distance has previously been demonstrated. However, not all polymers have similar degrees of intermolecular ordering, and the effect of this on dynamics is unknown. Further, intermolecular ordering shifts depending on environment, and the effect of this is unknown as well. To achieve the objectives stated above, a series of polymers, wherein the degree of intermolecular ordering ranges from very little to extensive will be considered. A given polymer [A] will then be considered in a series of second components [B]. Changes in the degree of intermolecular ordering will be observed, including the original polymer [A-A], and the new ordering [A-B} induced by the changing environment. Observations will be made by coherent neutron scattering, which reveals relative motion on selected spatial scales, and molecular simulation, will assess the location and extent of spatial separations relevant to interchain packing. This combination of techniques has been chosen because they can follow relative motion with spatial selectivity. The ability of neutron measurements to select for spatial scales will be exploited to separate the contributions of the a and b-relaxations, and assess the influence of environment of each individually. The novelty of the proposal lies in following relative, rather than self motion, investigating carefully selected series of materials, and integrating molecular simulation. This work, when completed, will allow us to connect features intermolecular packing with relative motion, and to unambiguously delineate the role of environment in miscible blend dynamics.%%%Educational activities are centered on bringing research-oriented activities to students who would not otherwise have these experiences. Specifically, open-ended experimental/simulation problems will be introduced in core chemical engineering courses, research opportunities will be provided to students in non-research universities, and a senior elective course on molecular simulation and its role alongside experiment will be added to the Chemical Engineering curriculum. Selected undergraduate students entering their senior year at Cal Poly Pomona, and industrially oriented university with no formal research program, will be invited to spend a summer pursuing research in the PI's group. The students' research will continue as their senior thesis project during their final year. These students will develop a course project based on the research they conduct at Penn State. At the same time, open-ended projects will be developed and used in the reaction engineering and thermodynamics courses, and an experiment with a simulation comp0nent will be added to the senior laboratory course. These projects will be compiled, and in the last year of the Plan, used as modules in a senior elective course. This course, aimed at non-simulators, will teach students how to use and interpret simulation data, much as a traditional laboratory course does the same for experimental data.The research to be carried out in this proposal falls in the general area of short-time dynamic behavior in polymer melts and blends, an area important for its relevance to the glass transition and processing behavior of these common materials.